1. FIELD OF THE INVENTION
The present invention relates to an electrophotographic photosensitive member, particularly an electrophotographic photosensitive plate having high sensitivity to rays of long wavelengths of about 800 nm that correspond to the oscillation frequency region of diode lasers.
2. STATEMENT OF THE RELATED ART
There is a conventional type of electrophotographic plate which comprises a selenium (Se) film about 50 .mu.m thick formed by vacuum deposition on an electroconductive substrate such as an aluminum substrate. However, this Se plate has disadvantages such as the spectral sensitivity thereof limited to wavelengths of up to about 500 nm. Another conventional type of photosensitive member comprises an Se layer about 50 .mu.m thick formed on a conductive substrate and further a selenium-tellurium (Se-Te) alloy layer several .mu.m thick formed on the Se layer. While the spectral sensitivity of this photosensitive member extends to a longer wavelength as the Te content of the Se-Te alloy is increased, this increase in the Te content raises the serious problem of impairing the ability to retain the surface electric charge, making it practically impossible to use the photosensitive member.
On the other hand, there is a so-called complex double layer type of photosensitive member which is produced by applying chlorocyanine blue or a squarium acid derivative on an aluminum substrate to form a charge generation layer about 1 .mu.m thick and then applying a material of high insulation resistance such as polyvinylcarbazole or a pyrazoline derivative-polycarbonate resin mixture on the charge generation layer to form a charge transport layer from 10 to 20 .mu.m thick. But, this type of photosensitive member does not have sensitivity to rays of longer wavelengths than 700 nm.
Moreover, there is known a complex double layer type of photosensitive member corrected in the above noted drawback, that is, photosensitive members having sensitivity to rays of about 800-nm wavelengths that correspond to the oscillation frequencies of diode lasers. Most of these photosensitive members are provided with sensitivities to longer wavelengths by the vacuum deposition of a metal phthalocyanine having a group III or IV metal of the periodic table as a central metal to form an about 1-.mu.m thin film, and dipping it in a shifting agent solution or contacting with a shifting agent vapor to shift the absorption band originally of about 700 nm to around 800 nm.
This thin film is coated with a 10- to 20-.mu.m thick charge transport layer of a material of high insulation resistance such as polyvinylcarbazole or a mixture of a pyrazoline or hydrazone derivative with a polycarbonate or polyester resin, thereby making up a complex double layer type of photosensitive member.
However, this type of photosensitive member involves a significant problem. That is, the thin film, serving as a charge generation layer, formed of a metal phthalocyanine having a group III or IV metal as a central atom, has essentially no absorption at about 800 nm that corresponds to the oscillation frequency region of diode lasers. Hence, the photosensitive member comprising said thin film as a charge generation layer does not have sensitivity or has low sensitivity to rays of about 800-nm wavelengths, unless the film is treated with a shifting agent (see U.S. Pat. No. 4,426,434).
In recent years, a number of attempts have been made to apply diode lasers as light sources to laser beam printers and the like, wherein lasers other than diode lasers have been used as light sources and electrophotographic plates have been used. Since the wavelengths of rays from the light sources are around 800 nm in these attempts, there is strong demand for an electrophotographic plate having high sensitivity to rays of long wavelengths of about 800 nm.